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Computer science A level > The internet > Flashcards

The internet Flashcards

1
Q

what is the internet

A

a network of interconnected networks set up to allow computers to communicate with each other globally

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2
Q

when can the internet be used without the world wide web

A
  • using email protocols like SMTP to send messages and IMAP to receive them
  • file sharing
  • voice calls
  • gaming
  • messaging apps
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3
Q

structure of the internet - backbone

A
  • the main part of the internet
  • set of dedicated connections that connect several large networks at various parts of the globe
  • each of these points are then connected to other regional networks
  • usually controlled by ISPS (internet service providers)
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4
Q

what are ISPs

A

Internet service providers
- connect to the backbone
- distribute/sell the internet connection to smaller providers
- who then provide access to individual end users/homes

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5
Q

structure of the internet - internet addresses

A
  • each device on a network needs to be uniquely identified so that data can be sent to the correct destination
  • internet addresses are unique numerical or alphanumerical identifiers used to identify devices or websites on the internet
  • they use the IP address system
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6
Q

structure of the internet - internet registries

A
  • ensure that a particular domain name is only used by one organisation
  • provides a marketplace for available domain names
  • managed domain names, dispute resolution services
  • registers individual or company details
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7
Q

Structure of the internet - URL’s

A

A UNIFORM RESOURCE LOCATER is the full address for an internet resource.
it specifies the location/address of a resource on the internet

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8
Q

Structure of the internet - Domain names and the Domain name system

A

a domain nameidentifies the area or domain that an internet resource resides in
- these are structured into a hierarchy of smaller domains

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9
Q

what is a fully qualified domain name

A

one that includes the host server name, eg www, mail,
- www.blahblah.com

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10
Q

structure of the internet - IP addresses

A
  • is a unique address that is assigned to a network device
  • indicates where a packet of data is to be sent or has been sent from
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11
Q

describe the main purpose of the DNS system and how it works

A

HOW IT WORKS:
- DNS stores a database of fully qualified domain names and corresponding IP addresses
- DNS is a* distributed database of mappings*
- individual mappings are only known by some DNS servers
- DNS servers are ordered into a hierarchy

PURPOSE:
- Translates fully qualified domain names into IP addresses

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12
Q

what is circuit switching

A
  • creating a communication connecting two endpoints for the duration of a phone call or transfer of data
  • but wasnt scalable, so packet switching was created
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13
Q

what is packet switching

A
  • communicating packets of data across a network
  • where other similar communications are happening simultaneously
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14
Q

what are data packets
how many bytes of data does each packet usually contain?
what does each packet contain?

A

equal sized chunks that data is broken up into when sending data across a network
- each packet typically contains 1,500 bytes of data
- each packet contains a header and a payload containing the body of data being sent
- some packets may also use a trailer with a checksum

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15
Q

advantages of data packets

A

increases network efficiency and reliability

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16
Q

what is a checksum

Outline how the checksum’s value will be determined

A
  • Something to check if the contents of the
    packet have been corrupted during transmission
  • Calculated from the
    payload of the packet
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17
Q

what is the header

A

includes:
- the senders and recipients IP addresses
- the protocol being used in the packet
- the number of the packet in the sequence being sent
- also include the hop limit/time to live
- packet length

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18
Q

what is the hop limit or TTL(time to live)

A

the point at which the data packet expires and is discarded

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19
Q

why is the senders IP address included in the packet header

A
  • in order to identify the sender
  • to send a request back to the sender if it contains data transmission errors
  • to notify the sender if the packet cannot be delivered.
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20
Q

what do routers do

A
  • Connects two networks together
  • determines which node to send packet to next
  • Router uses most efficient path to the destination
  • Router modifies the (MAC/hardware) addresses for the next hop
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21
Q

what is a hop

A

each forwarding by(or transfer across) a network

22
Q

what is a routing algorithm

A

used to find the optimum route

23
Q

what is a gateway
what is the functionality of a gateway beyond that of a router

A
  • a device that is required where data is travelling from one network to another that use different protocols
  • networks using different transmission media can require this

2.protocol conversion

24
Q

how does a gateway work

A
  • all of the header data is stripped from the packet, leaving only the raw data
  • the new header data is added in the format of the new network before the gateway sends the packet on its way
25
Q

packet size

A
  • kept small to ensure that individual packets do not take excessive time to transfer
  • preventing other packets from moving
  • However, they should not be too small, as the additional data added makes data transfer inefficient as unnecessary headers and trailers are used
26
Q

summarise the packet trailer

A
  • contains the error checking component (checksum)
27
Q

describe the operations of packet switching

A
  • data broken down into packets
  • source/destination IP is added to each packet
  • packet routed independently
  • packets reassembled into message
  • errors are checked for
  • if theres an error, request for corrupted packets to be resent
28
Q

what is a firewall

A

a software or hardware that controls access to and from a network
- it prevents unauthorised access between two networks

29
Q

what does a firewall consist of

A
  • a separate computer with 2 NICs(network interface cards), with one connected to the trusted network, and the other connected to the external one
30
Q

what is a port

A

gates that only certain types of traffic is allowed to pass through, dependent on its IP addresses

31
Q

summarise packet filtering

A
  • packets of data are inspected by the firewall to check which point they want to access
  • different protocols use different numbers
  • if this traffic is allowed through, the port must be opened for the duration of the connection
  • otherwise, the firewall will automatically reject it
32
Q

what does packet filtering do

A

controls network access according to network administrator rules and policies
- by examining the source and destination IP addresses in packet header

33
Q

what port does HTTP traffic use

A

80 or 808

34
Q

What is stateful inspection in a firewall

A
  • used instead of relying on port numbers or IP addresses
  • it examines the payload of a packet to better assess it for safety, before allowing access
    -tracks the state of active connections and allows packets that are part of an established connection.
35
Q

meaning of proxy

A

on behalf of

36
Q

what is a proxy server

A
  • makes a web request on behalf of your own computer
  • intercepts all packets entering and leaving a network
  • **hides the true network address **of the source from the recipient
37
Q

advantages of a proxy server

A
  • enables privacy
  • can be used to filter undesirable content
  • logs user data with their requests
  • enables anonymous surfing
  • can maintain a cache of websites commonly visited to speed access times
38
Q

what is encryptionnn

A

the act of encoding a plaintext msg so that it cannot be deciphered unless unless u have a key to decrypt it

39
Q

what is symmetric encryption

A

when the same key is used to encrypt and decrypt

40
Q

risks of using symmetric encryption

A
  • If either party loses the key or it is stolen, the system is broken. If the key is also intercepted along with the data, the message can be deciphered.
  1. Man-in-the-Middle (MITM) Attack:
    - During key exchange, an attacker intercepts the shared key and decrypts the communication.
    - Complete compromise of confidentiality and privacy; attackers can read or alter data undetected.
41
Q

what is asymmetric encryption

A

using separate but related keys

42
Q

summarise asymmetric encryption

A
  • the public key is made public so that others can send data and encrypt the data
  • public key CANNOT decrypt data
  • a private key is known only by you and can be used to decrypt data
  • impossible to deduce the private key from the public key
43
Q

how does a digital signature work

A
  1. sender applies hashing algorithm to message to create a hash value
  2. hash calculated from message text
  3. hash encrypted using senders private key
  4. creates digital signature
  5. signature appended to message
  6. message with signature needs to be encrypted using receivers public key
  7. signature decrypted using senders private key
  8. hash value recalculated and compared
  9. A match is accepted as genuine
44
Q

what is a digital signature

A

a security stamp that offers greater security

45
Q

what is a digital certificate

A

something that verifies that a senders public key is formally registered to that particular sender

46
Q

features of a digital certificate

A
  • issued by the CA(Certificate authorities)
    contains:
  • serial number
  • expiry date
  • subjects public key
  • name id the CA
47
Q

what does a firewall do

A
  • blocks/allows traffic on specific ports
  • blocks specific protocols
  • blocks specific IP addresses
  • Blocks/allows certain types of packets
  • acts as a proxy server
  • identifies unusual behaviour from hosts
48
Q
  1. Why is packet switching used?
  2. What is the role of routers in packet switching?
A
  • Packet switching breaks data into packets and routes them independently across a network for efficient use of resources.
  • Routers forward packets to their destination by analyzing their headers and choosing the optimal path.
49
Q

What is the purpose of a digital signature

A

To verify the authenticity and integrity of a message.

50
Q

difference between well known ports and client ports

A

Well-known ports are ports that have a specific purpose like HTTP and FTP.

Client ports are temporary ports used by devices to establish connections with servers.

51
Q

what other things are included in a data packet

A

Port number(s);
destination port number and source port number as separate marks
Sequence number;
Time to live;
Packet size/length;
Type of service;
Protocol identifier;
Packet identifier/ID number;
IP version;
Options/Padding;
Flags;
Window size value;
Fragment offset // header length;

Computer science A level (33 decks)

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